Bore sighting error detector



June 24, 1958 E. BAILEY, JR 2,840,810

BORESIGHTING ERROR DETECTOR Filed May 8. 1946 PICHKJRUNP 4 II I I I I0 I 25-50 VARIABLE TRANSMITTER COU PLER ATTENUATOR 13 (I8 I? 16 |5 INDICATOR" VIDEO cRYsTAI. |ND|ATR AMPLIFIER AMPLIFIER DETECTOR l TRANSMITTER couPLER J as VARIABLE 2 ATTENUATOR CRYSTAL I DETECTOR INDICATOR f I VIDEO INDICATOR AMPLIFIER AMPLIFIER TRANSM|TTER- couPLER TRANSMIT FIG 3 REcEIvE BOX I VARIABLE VIDEO INDICATOR I ATTENUATOR AM PUHER AMPLIFIER IN DICATORI IMvEMToR EDWIN M. BAILEY,JR. CRYSTAL DETECTOR BY ATTORNEY mesne assignments, to the iUnited-Statesof America .as representedby the ,Secretaryof .the. NaYy Application May 8,1946; SerialNo. 5668;028 .3 Claims. cha ts-i117 This invention relates to ,'electrical apparatusandmore particularly to a detecting system for measuringboresighting errors in radar ;controlle'd gun-1aying.equipment.

In radar controlled guni-laying equipment, .a transmitter sends out a series of"h igh'"freque ncy pulses using a parabolic reflector as a radiating 'element'to cause conical. scanning of the 'radiatiompattern. In a conical scan system the axis ofzthe radiated beam describes a cone in space. A .target in the zone covered by 'the searching beam reflects a signal which.is; picked'up'by the same antenna. The scanning of 'the radar 'beam produces a modulation'of the reflected signal, the amplitude of which indicates how far thetarget is vofi'the axis of,the;spinning antenna, andthe scanning phase of which determines thedirection in which'the 'targetisofi the axis of-the antenna. -Suitable receiving 'and=tracl-;ing

units are employed :to adjust the position ofthe antenna so 'that ;its axis .points directly at the L'target causing States Patent- *amplifier 17 0f the;same model as used-with --the-transthe 'fundamentalmodulation ofthe signal reflected from the target to go-to "zero. The guns of the systemare mechanically linked to the antenna in such a manner rection as the axis of the radar antenna. "In'a'd'dition, the system has a tracking andarnplifiersystem following the receiver of the radar system which analyzes this fundamental modulation -both in-arnplitude ,and phase, "and presents this information on aeathode=ray tube indicator which shows range -and-angular deviation of the {chosen target. This typeof-indicatorconveysito the ggunnerthe required information for -firing -the 'guns at the proper time. i

However, reflections set upduring-the scanningof the antenna cause pulling -of-the *transniitter power "and frequency. Pulling is the term applied to external factors affecting the amplitude and frequency of the electromagnetic energy generated in the transmitter. This pulling effect causes returned signals to be modulated even when the target is directly on the axis of the radar scan. Since the tracking system acts to position the antenna as long as there is a modulating signal, an error in the pointing of the antenna, and hence its associated guns, results. It is desirable to determine the magnitude and direction of this boresighting error due to pulling, so

that corrections can be applied to the mounting of the guns relative to the antenna to overcome this error.

Accordingly, the primary object of the present inveny tion is to provide a method of measuring boresighting errors due to frequency and amplitude pulling of the radar transmitter used in gun-laying radar systems.

Another object of the present invention is 'to provide electronic apparatus to measure bearing deviation caused by pulling of transmitter frequency in radar controlled gun-laying systems.

A further object of the present invention is to provide a method of determining the filtering action of a IT-R box, or transmit-receive switch.

that the guns are at all times pointing in the,same di--,

2,840,810 Patented June 24, 1958 (in measuring boresighting e'rrors';

Figure? 2 is a block 'diagram'pf {the circuit "consisting ;of' Figure l as -appliedfor thearreasurement tifizoresight- 'ing errors; "and g I t Figure 3- is the-systemof' Figureincluding -a T-i-"R 'b'ox =ortransmit receiveswitch. I

"Referring to Figure -l, the system-to be tested tconsists of 'a transmitter 10, a directional "coupler "1:1 and directional,spinnerantenna 1'2. "The-*test-'equipment:tobe "calibrated consists of a pick-up ihorn 13, attenuator "14, crystal -detector 15, video amplifier 16, an findicatormitter to complete "the gun laying system, andga 'rafdar indicator 18=s 1ch as{that-desciibeklalrove The purpose *of this-apparatusis to=determine the sensitivity in mils angular deviation per "inch defiectiori 'on "the indicator screen; 7 sensitivity is' determinedbrmovingthe fantenna assembly by a known angle @whilepointing] at *aitar'gt. The target -'in "this case "is pickup'-horn l 3iilocated between 25 and'SO- feet {from the antenna w hich feeds into attenuator 1 4 and crystal detector '15. The "output; of

- cator-amplifier 17 'analyzes the amount of "modulation which results frompointing the antenna offjtargetl The amount of deflection of the-=spoton-thefface of in'rlicator 18 is compared with the known"angular-shift pf the- '7 "mechanism that accomplishes thefl'scanning jof antenna 12. 'jFor example, theoutput of a rotary -tran$former drivenfrom -the :antenna -sca-nriing apparatus can serve as :this -reference=signal. v i I a The present-invention provides -a -me'tho'd by which rthercomp onentsr described above-are utilizedier detecting 'zhoresighting: errors :due: to frequency and -amplitude* pulling ofgthe transmitter power. Again, referring to Figure 2, the system under investigation consists of transmitter 20 and directional antenna 21. A directional coupler 22 is used to sample power from transmitter 20, which may or may not be pulled in frequency or amplitude due to varying reflection from'antenna 21. Antenna 21 is point-- ed intofree space with no targets in the vicinity so that no modulation will result from from a target. Energy from directional coupler 22 feeds through attenuator 23, crystal detector 24, video amplifier 25, and then into the analyzing amplifier 26 and indicator 27 of the gun directing system. It is im- The foregoing and other objects of the presentinvenportant that attenuator 23 be adjusted sucli that the 'signal is not so strong as to cause crystal or amplifier saturation which vwould result in a loss of modulation indication. V of modulation due to pulling, and the boresighting error which results is indicated by the amount of deflection of the spot on indicator 27, the sensitivity of whichwas determined as described above with reference to Figure I 1. Since the antenna is pointed into space free from. targets, if there is no indication of modulation, there is 7 no pulling. If pulling is present, the boresighting error causedby it can be determined and corrective steps can be taken to overcome the error.

energy being returned Indicator-amplifier 26 3 analyzes theamount it will be seen from the above that the equipment of Fig. 1 is used solely to calibrate the cathode ray tube indicator, and any effects of transmitter pulling are compensated for in the initial balancing of the system. The

circuit of Fig. 2 is similar to that of Fig. 1 exceptfor 5 thefact that the indicator 27 is directly supplied with a portion of the transmitted power by means ofthe performance of directional coupler 22. It should be appreciated that the components of Fig. l are conventional radar assemblies which are interconnected for the purl0 pose of calibrating indicator 18. Presumably, the calibration of indictor18 applies with almost equal accuracy to similar indicators. If one adopts this position, Fig. 2: may represent a difierent radar system. However,

there is no reason why the components of'Figs. 1 and'2 cannot be the'same that is, the cathode ray tube of a particular radar system can be calibrated by the method ,shown in Fig. 1' and then this system tested for pullingby the arrangement of' Fig. 2. In the latter case, of

course, it isonly necessary to feed first the crystal de- 20 tector from a directional horn illuminated by the scanning beam'and thenfrom a directional coupler inserted between the transmitter and the antenna.

V A further application of this procedure is to determine the efiect of the filtering action of a transmit-receive 2 switch, ;which is commonly known in the art as a T-R box. In Figure- 3, a T- -R 'box 28 is shown inserted'between the directional coupler and the attenuator of the icircuit described in connection with :Figure' 2. When the T Rbo); is detnned the-spot deflection on indicator 29 30 changesbecause frequency pulling is turned into change in amplitude since the attenuation through; the T R box changes .withfrequency. t g

The procedure outlined in the foregoing'specification need not be limited tothe applications mentionedwhich are considered as illustrative of a formthe invention may take.- What is claimed is: r

1. A circuit for determining the filtering action 0 z'fl transmit-receive switch as used in radar systems comprising, a directionalcoupler coupled to said radar system for sampling power from each transmission of said radar system :transmitter, the output of said coupler? being said modulation detector circuit.

2. A circuit for determining the error introduced by a transmit-receive switch used in a radar system including a transmitter and an antenna coupled to said transmitter, said circuit comprising a directional coupler coupled to said radar system at a point intermediate said transmitter and said antenna, said directional coupler sampling power from each transmission of said radar system transmitter, a transmit-receive switch coupled at its input to the output of'said directional coupler, a variable attenuator, means coupled by said attenuator to the output of said transmit-receive; switch for detecting the signal from said transmit-receive switch while preserving the amplitude modulation present thereon, amodulation detector circuit coupled to said detecting means, said modulation detector circuit being adapted to produce an output proportional to saidamplitude modulation and an indicator coupled to said modulation detector circuit for indicating the amplitude of the output therefrom;

3. A circuit for detecting frequency and amplitude modulation of thetransmitted signal in a conically scanning radar system including at least a transmitter and an antenna, said circuit comprising a directional coupler coupled to said radar system intermediate said transmitter said antenna, said directional coupler sampling power from eachtransmission of said radar system translmitter, a variable attenuator coupled to the output of said directional coupler ,for reducing the magnitude of saidpower sample, means coupled to the output of said 'variable" attenuator for detecting the signal from said attenuating means while preserving the amplitude modu- "lation present thereon, a modulation detecting means, said'niodulation detecting means being adapted to projduce an output proportional to said amplitude modulaj'tiori and an indicator coupled to said modulation de- 'tecting means for indicating the amplitude of the output efr m a y V -References Cited in the file of this patent V UNITED STATES PATENTS 1,924,174 Wolf Aug. 29, 1933 2,050,418 Boerner Aug. 11, 1936 2,268,643 Crosby Jan. ,6, 1942 2,418,143 StOdOIa Apr. 1, 1947 2,479,222 Edlen u Aug. 16, 1949 2,505,525 Clapp Apr. 25, 1950 2,532,539 Counter Dec. 5, 1950 2,549,385

:Rapriano Apr. 17, 1951 

